Electrochemical processes of producing manganese from aqueous manganese salt solution



Feb. 20, 1951 FROM AQUEOUS MANGANESE SALT SOLUTION Filed Nov. 28, 1945 E. ABEL ELECTROCHEMICAL PROCESSES 0F PRODUCING MANGANESE V6!) for Patented Feb. 20, 1951 ELECTROCHEMICAL PROCESSES OF PRO- DUCING MANGANESE FROM AQUEOUS MANGANESE SALT SOLUTION Emil Abel, London, England, assignor to The Ever Ready Company (Great Britain) Limited; London, England, a British company Application November 28, 1945, Serial'No. 631,286 In Great Britain September 14, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires September ,14, 196.4

1 6 Claims.

This invention relates to el'ectro-chemical processes of producing manganese from aqueous manganese salt solution.

In the usual commercial electro-chemical processes for producing manganese metal from aqueous solutions of manganese sulphate (MDSO4) the anode is usually of lead and the cathode of stainless steel. A mixed electrolyte of a low manganese content, usually containing ammonium sulphate in a rather high concern tration is used, to which, moreover, various other substances had to be added. The pH had to be maintained atv about 68. The electro-chemical process is usually carried out at a low temperature, for example room temperature.

Manganese is more electropositive than most heavy metals in relation to hydrogen, and has an electro motive force of approximately 1.1 volts measured against hydrogen Moreover, since the working conditions must be such as to prevent the formation of manganese oxides, this enforces a range of concentrations of hydrogen ion which favours the competitive deposition of hydrogen, and hence the process is most uneconomical, as during the process the current employed produces manganese and hydrogen in somewhat similar quantities. From the point oiyiew of current consumption the efficiency is hardly-more than 50%. To prevent the anodic products of electrolysis, higher oxides of manganese at the anode, and especially sulphuric acid, reaching the manganese on thecathode, porous diaphragms, have been interposed between the anodes and cathodes.

The main object of the present invention is to simplify the industrial process of producing the metal manganese and to make it far more economical.

A further main object is to produce manganese dioxide at the same time as the manganese metal.

In accordance with the present invention-the cathode or the cathodic surface is formedof such a substance, or-is influenced by or during the electrolysis in such a way that hydrogenhas' a permanent high overvoltage on the cathode during the process, such that the dischargeof manganese ions is facilitated.

With sufficient overvoltage, displacement of the hydrogen voltage as compared with that of the manganese metal can be so great that manganese metal is so much more easily deposited than hydrogen that manganese deposition can take place almost without any hydrogen deposi tion, hence fromtthe point of view of current em of manganese metal and manganese dioxide,

which have hitherto been necessarily produced independently of each other, since the electrochemical production of manganese dioxide requires a hot solution, preferably at a temperature between 80 C. and 100 0., and produces sulphuric acid in an increased quantity, according to the equation.

Whereas in the previous processes for the production of manganese metal the pH of the solutions had to be maintained at'ab'out 6-B, in the process accordingto the present invention the solutions may be so strongly acid that the pH is about 1.

, Moreover, against the limitation previously imposed on the concentration of manganese salt solutions for the electro-chemical production of manganese metal in processes according to the present-inventionno limit is set to the concentration'of manganese salts in the electrolyte. Further, a pure solution of manganese salts can take the place of the mixed electrolyte heretofore used, and further, the various additions to the electrolyte which have hitherto been necessary to obtain manganese metal to a technically acceptable degree' are shown to be superfluous.

In carrying out the present invention there is no need to separate cathode and anode compartments so that the great advantage is achieved of being able to'carry out elsctroylsis unimpedzdly, that is withoutv porous diaphragms, producing, accordingto requirements, manganese metal, or the metal and manganese dioxide simultaneously.

The high overvoltage conditions are obtained, for instance, when the cathodic deposition of manganesemetal takes place usin liquid meronly as a cathode.

In carrying out processes, according to the invention, of producing manganese metal, or of producing simultaneously the metal and man-- ganese dioxide, the high overvoltage of the cathode may easily bereduced if the form of the original cathodic surface is altered in the process of electrolysis: owing. to the deposition of manganese. Thislis especially true with a cathode formed of liquid mercury. With the formation of the manganese amalgam in the liquid mercury the necessary overvoltage quickly disappears probably because the manganese amalgam which is formed on the surface remains there due to its lower density and destroys this overvoltage.

With the present invention it has been possible to counteract this behaviour and to achieve a continuous production of manganese with undiminished current efficiency constantly maintaining a high ov-ervoltage even on liquid mercury and with pure manganese salt solutions.

This result may be achieved with high cathodic current densities (e. g. 80-120 amps. per sq.

it. have been found advantageous) and by presenting fresh mercury surfaces as frequently as are more easily discharged by the electric current, than the hydrogen ions (forming hydrogen gas). The immediate effector this behaviour is the achievement of a hitherto unobtained current efficiency in electro-chemical manganese production, nearly twice the values previously reached.

and the like,

By these means it is possible to conduct the electro-chemical production of manganese metal, with or without the simultaneous production of manganese dioxide, in such a way, that on the one hand the electrolyte is stripped of its manganese contentto a considerable degree, and on the other hand the cathodic surface is substantially completely utilised. This latter fact is especially valuable, if, according to the present invention, the high overvoltage is obtained by using mercury. ,Even when using liquid mercury its amount is considerably reduced in relation to the quantity of manganese metal produced.

In order to indicate how the invention can be carried into effect preferred embodiments will now be described by way of example with reference to the accompanying drawings which show apparatus therefor.

In the drawings which show the apparatus somewhat digrammatically- Figure l is a side elevation,

Figure 2 is an end elevation from the left of Figure 1 and Figure 3 is a plan, of an electrodeposition tank according to the invention.

The apparatus illustrated comprises a rectangular tank l of, for example, ferrous metal coated with lead or rubber, having an inlet pipe 2 and an outlet pipe 3 for the electrolyte. Extending above and longitudinally of the tank is a series of clamping bars 4 between each pair of which is held a downwardly depending sheet of lead 5, together constituting the anodes. The clamping bars are connected at one end by a bus bar Bto which is connectedthe positive cable 1. As seen best in Figure 2 the lead sheets 5 are deeper at the sides than in the middle of the tank.

In the bottom of the tank and extending throughout almost its whole length is a trough 8 7 made of ebonite or rubber or any similar nonconducting material. This trough is to hold the mercury which is introduced through the inlet pipe 9 and constantly drawn off through the outvlet pipe i0 into the outlet tank H. The mercury received in the tank may, except for a small portion, be returned by a pump to the inlet 9 and manganese may be removed from the mercury before returning it to the inlet 9. Thereby a rapid circulation of the mercury may be maintained. The pipes 9 and H) where they extend between the trough and tank ends are protected from the acidic solution by lead or rubber sheaths I2, and the outlet pipe it is connected to the negative cable is so that the mercury in the trough forms the cathode.

In the bottom of the tank I unoccupied by the trough 8 is a steam heater coil. M by means of which the temperature of the electrolyte can be 7 controlled as required. 7 Depending into the tank are three vertica shafts i5 driven by gearing from a drive shaft l6 and carrying at their lower ends stirrers, made for example of rubber-covered stainless steel and each comprising a lower series of blades I1 situated in the trough 8, and an upper series of blades l8 situated above the trough 8 and below the lower edges of the shorter, middle lead anode trough 3 as the cathode, at room temperature 7 with a current density of about 90 amps. per sq. ft., the potential difference between the two electrodes being 4.54.5 volts.

At theanodes 5 oxygen is evolved mainly; the higher manganese oxides which are, in addition, formed in small quantities are prevented from reaching the cathode by wrapping the anode in a thin cloth (not shown) which does not act as a diaphragm, but serves only, to retain the suspended matter. The electrolyte is well stirred as above described and its acid content is about 10 gr. H2SO4 per litre. The current efliciency is about 90%.

The resulting sulphuric acid is a valuable byproduct and may be used to advantage in a cyclic process to leach new manganese ore and in this way to regenerate the manganese sulphate in proportion to its impoverishment. Under the conditions described about 400 lbs. manganese metal are produced per 1000 kwh. besides 700 lbs. sulphuric acid.

If, simultaneously, manganese metal and manganese dioxide are to be produced, the same solution of manganese sulphate as just described is electrolysed between the same electrodes at a temperature of about C. which is maintained by the steam coil id. The current density at the cathode will be kept higher than at the anode, for example, the former at amps. per sq. ft., the latter at 15 amps. per sq. ft., potential 3-4 volts. Current efficiencies at cathode and anode are roughly equal and round about 85%. The electrolyte is again well stirred as above indicated and its acid content is about 15 grpI-IzSOr per litre. Again the mercury is agitated and cir-' culated, and the resulting sulphuric acid is produced according to the equation previously stated, and is-used ina cyclic process as described. Manganese is deposited on the mercury cathode and on the anode manganese dioxide is deposited with a M1102 content of about 90%. About 550 lbs. manganese metal and 950 lbs. manganese dioxide are produced per 1000 kwh. besides 1950 lbs. sulphuric acid.

By the present invention a very efiicient process or" production is achieved in comparison with the industrial process at present employed.

It may be repeated that whereas in the known industrial process the current efficiency is only about 50% in processes according to the present invention efliciency of over 90% can be achieved, and this advantage is due to employing a cathode which has a high overvoltage as compared with hydrogen.

It will also be appreciated that in carrying out the present invention the formation of acid in solution is not a disadvantage whereas in the known process it is necessary to take steps to maintain the solution at a pH of about 7.

By the present invention a very simple process is devised of producing manganese metal and artificial activated manganese dioxide, the manganese metal being suitable for incorporation in non-ferrous alloys to increase their tensile strength, and for improving steel.

I claim:

1. In the electro-deposition of manganese from aqueous manganese salt solutions, using a liquid mercury cathode, the improvement comprising electrolyzing a manganese salt solution having a pH of about 1, in the absence of a dia hragm, establishing a current density at the cathode of about 80 to 120 amperes per square foot and agitating the liquid mercury cathode during said electro-deposition, whereby a continually fresh mercury cathode surface is presented and a perm'anent high overvoltage is imparted to the hydrogen, thereby causing free deposition on the cathode of the liberated manganese.

2. In the electro-deposition of manganese from aqueous manganese salt solutions, using a liquid mercury cathode, the improvement comprising electrolyzing a manganese salt solution having a pH of about 1, in the absence of a diaphragm, establishing a voltage of between 4.5 and 5.5 and a current density at the cathode of about 80 to 120 amperes per square foot and agitating the liquid mercury cathode during said electrodeposition, whereby a continually fresh mercury cathode surface is presented and a permanent ,high over voltage is imparted to the hydrogen,

thereby causing free deposition on the cathode of the liberated manganese.

3. In the electro-deposition of manganese and manganese dioxide from aqueous manganese salt solutions, using a liquid mercury cathode, the improvement comprising electrolyzing a manganese salt solution having a pH of about 1, in the absence of a diaphragm, at a temperature of from 80 to 100 0., establishing a current density at the cathode of about 80 to 120 amperes per square foot and agitating the liquid mercury during said electro-deposition, whereby a continually fresh mercury cathode surface is presented and a permanent high over voltage is imparted to the hy drogen, thereby causing free deposition on the cathode of the liberated manganese and on the anode of the manganese dioxide.

4. In the electro-deposition of manganese and manganese dioxide from aqueous manganese salt solutions, using a liquid mercury cathode, the improvement comprising electrolyzing a manganese salt solution having a pH of about 1, in the absence of a diaphragm, at a temperature of 85 C., establishing a voltage of 3 to 4 and a current density at the cathode of about to 120 amperes per square foot and agitating the liquid mercury cathode during said electro-deposition, whereby a continually fresh mercury cathode surface is presented and a permanent high over voltage is imparted to the hydrogen, thereby causing free deposition on the cathode of the liberated manganese and on the anode of the manganese dioxide.

5. In the electrodeposition of manganese and manganese dioxide from aqueous manganese salt solutions, using a liquid mercury cathode, the improvement comprising electrolyzing a manganese sulphate solution having a pH of about 1, in the absence of a diaphragm, at a temperature of C., establishing a voltage of 3 to 4 and a current density at the cathode of about 80 to 120 amperes per square foot and agitating the liquid mercury cathode during said electrodeposition, whereby a continually fresh mercury cathode surface is presented and a permanent high over voltage is imparted to the hydrogen, thereby causing free deposition on the cathode of the liberated manganese and on the anode of the manganese dioxide.

6. In the electrodeposition of manganese from aqueous manganese salt solutions, using a liquid mercury cathode, the improvement comprising electrolyzing a strongly acidic manganese salt solution at 80 to C. in the absence of a diaphragm, establishing a current density at the cathode of about 80 to amperes per square foot and agitating the liquid mercury cathode during said electrodeposition, whereby a continually fresh mercury cathode surface is presented and a permanent high over voltage is imparted to the hydrogen at the cathode thereby causing free .deposition thereon of the liberated manganese.

EMIL ABEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 597,820 Keith Jan. 25, 1898 734,499 Baker et a1 July 28, 1903 1,304,222 Van Arsdale et a1. May 20, 1919 1,874,827 Storey Aug. 30, 1932 1,970,973 Palmaer Aug. 21, 1934 2,224,814 Gilbert Dec. 10, 1940 2,356,515 Guareschi Aug. 22, 1944 2,417,259 Mitchell et al. Mar. 11, 1947 OTHER REFERENCES Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 12 (1932), pp. 166-167.

Van Arsdale et al., Transactions Electrochemical Society, vol. 33 (1918), pp. 109-129.

Chemical Abstracts, vol. 36 (1942), p. 1851.

Zeitschrift fur Analytische Chemie, vol. 107 (1936), pp. 104-107. 

1. IN THE ELECTRO-DEPOSITION OF MANGANESE FROM AQUEOUS MANGANESE SALT SOLUTIONS, USING A LIQUID MERCURY CATHODE, THE IMPROVEMENT COMPRISING ELECTROLYZING A MANGANESE SALT SOLUTION HAVING A PH OF ABOUT 1, IN THE ABSENCE OF A DIAPHRAGM, ESTABLISHING A CURRENT DENSITY AT THE CATHODE OF ABOUT 80 TO 120 AMPERES PER SQUARE FOOT AND AGITATING THE LIQUID MERCURY CATHODE DURING SAID ELECTRO-DEPOSITION, WHEREBY A CONTINUALLY FRESH MERCURY CATHODE SURFACE IS PRESENTED AND A PERMANENT HIGH OVERVOLTAGE IS IMPARTED TO THE HYDROGEN, THEREBY CAUSING FREE DEPOSITION ON THE CATHODE OF THE LIBERATED MANGANESE. 